Consistent hashing to a subset of nodes. It works like consistent hash,

but instead of mapping to a single node, we map to a subset of nodes.

rootfs/etc/nginx/lua/balancer.lua

@@ -5,6 +5,7 @@ local dns_util = require("util.dns")
 local configuration = require("configuration")
 local round_robin = require("balancer.round_robin")
 local chash = require("balancer.chash")
+local chashsubset = require("balancer.chashsubset")
 local sticky = require("balancer.sticky")
 local ewma = require("balancer.ewma")
 
@@ -17,6 +18,7 @@ local DEFAULT_LB_ALG = "round_robin"
 local IMPLEMENTATIONS = {
   round_robin = round_robin,
   chash = chash,
+  chashsubset = chashsubset,
   sticky = sticky,
   ewma = ewma,
 }
@@ -29,8 +31,12 @@ local function get_implementation(backend)
 
   if backend["sessionAffinityConfig"] and backend["sessionAffinityConfig"]["name"] == "cookie" then
     name = "sticky"
-  elseif backend["upstream-hash-by"] then
-    name = "chash"
+  elseif backend["upstreamHashByConfig"] and backend["upstreamHashByConfig"]["upstream-hash-by"] then
+    if backend["upstreamHashByConfig"]["upstream-hash-by-subset"] then
+      name = "chashsubset"
+    else
+      name = "chash"
+    end
   end
 
   local implementation = IMPLEMENTATIONS[name]